1. Field of the Invention
The present invention relates to an automatic steering system for a vehicle, for automatically parking the vehicle without recourse to a steering operation by a driver.
2. Description of the Prior Art
Automatic steering systems for vehicles are already known from Japanese Patent Application Laid-open Nos. 3-74256 and 4-55168 and the like. The automatic steering systems for vehicles utilize an actuator for a conventionally well-known electric power steering device, and are designed so that back parking and linear parking are automatically controlled by controlling the actuator based on the relationship between a distance of movement of the vehicle and a steering angle that has been previously stored.
In the known automatic steering system, when a driver operates a steering wheel during an automatic steering control operation and it is determined that the steering torque exceeds a previously set reference steering torque, the automatic steering control operation is discontinued.
However, there is a problem that if the determination is carried out only by comparing an output from a steering torque detecting means with the reference steering torque, the output from the steering torque detecting means may temporarily exceed the reference steering torque due to noise in the steering torque detecting means, or due to an inertial torque of the steering wheel when a tire contacts a bump in the road or a curb, or when an automatic steering operation is carried out through the actuator, and at each time, the automatic steering operation is discontinued. If the reference steering torque is set at a higher value in order to avoid such a disadvantage, there is a possibility that the automatic steering operation and the manual steering operation may interfere with each other to give a sense of incompatibility to the driver, and if the driver operates the steering wheel during the automatic steering control operation, the automatic steering control operation may not immediately be discontinued.